This invention relates to exhaust gas recirculation systen in internal combustion engines and more particularly to a valve assembly for controlling exhaust gas recirculation.
Recirculation of exhaust gases has been developed as a method for reducing formation of oxides of nitrogen (NOx) during the combustion process in an internal combustion engine. In general, it is desired to control exhaust gas recirculation in response to engine operating conditions, and a variety of control valves responsive to the engine operating conditions have been utilized for this purpose.
A valve responsive to exhaust gas pressure so as to recirculate the exhaust gases at a rate proportional to the rate at which combustion air (induction air) flows into the engine has been proposed by the same inventor as that of this application. This will be more particularly described hereinafter.
The exhaust gas recirculation control valve assembly which has been proposed by the same inventor utilizes a difference between a first pressure within an exhaust passage in a zone downstream of a first orifice provided in the exhaust passage downstream of an inlet port of an exhaust gas recirculation passage and a second pressure within the exhaust gas recirculation passage in a zone between a second orifice provided in the exhaust gas recirculation passage and an exhaust gas flow control valve member disposed in the exhaust gas recirculation passage downstream of the second orifice, so as to recirculate exhaust gases at a rate proportional to exhaust gas flow through the exhaust passage in order to recirculate exhaust gases at a rate proportional to air flow toward an engine. The valve is operated to keep this difference at a predetermined magnitude. The rate of recirculation of exhaust gases is thus proportional to the rate of exhaust gas flow through the exhaust passage. Since the rate of exhaust gas flow is proportional to the rate of induction air flow, exhaust gases can be recirculated at a rate proportional to induction air flow.
With this exhaust gas recirculation control valve assembly the exhaust gas flow control valve member is not directly operated by the member responsive to the difference between the first and second pressure; instead, the valve member is positioned by a member operated by an induction passage vacuum signal and the member responsive to the difference between the first and second pressure controls that signal.
In order to reduce the rate of recirculation of exhaust gases under engine operating condition at high speed with light load so as to maintain the engine stability under this condition, the member responsive to the difference between the first and second pressure is biased in such a manner as to assist movement of the member due to the first pressure by a member which is alternatively responsive to the control signal or atmosphere through a control valve.
Although with this exhaust gas recirculation control valve assembly the rate of recirculation of exhaust gases is proportional to the rate of exhaust gas flow through the exhaust gas passage there is a problem that the proportional relationship between the rate of recirculation of exhaust gas through the exhaust gas passage and the rate of induction air flow may be disturbed or broken such as when there occurs the pulsation of exhaust gases. Another problem is that the first orifice provided in the exhaust gas passage so as to reduce the effect of the pulsation of exhaust gases on the proportional relationship (the smaller is the effective flow area of the orifice provided in the exhaust passage, the better the precision of the proportional relationship between the rate of recirculation of exhaust gases and the rate of induction air) will cause a reduction in the maximum output of the engine by throttling exhaust gas flow through the exhaust gas passage. Still another problem is in that suitable measure must be taken to reduce the effect of the dirty deposit and the heat of the exhaust gases upon the component parts of the recirculation control valve assembly.